Flow meter

ABSTRACT

Flowmeter for locating zones containing currents in a bore hole made in a rock. The flowmeter comprises parting elements (1) for separating a measurement section (3) in the hole from the rest of the hole in a substantially pressure-tight manner; an open flow duct (4) forming a free flow link between the hole portions on opposite sides of the flowmeter past the measurement section; and a measuring duct (5) leading from the section under measurement to a point outside it, together with measuring equipment (6), for measuring the magnitude and direction of flow between the measurement section and the hole portion outside it.

BACKGROUND OF THE INVENTION

The present invention relates to a flowmeter designed to find areascontaining currents in a hole bored in rock.

In searching rocks via measurements in deep bore holes, a seriousproblem is the slowness of the measurements. Measuring only the verticalcurrent at a given depth in a hole provides practically no informationabout chinks at different depths in the rock or the magnitude anddirection of currents flowing in them. On the other hand, makingaccurate measurements e.g. by sections of a few hundred meters over thewhole length of the hole to obtain the flow rates and directions for thesection is a very slow process in long holes going to depths as large asthousands of meters.

As the bore hole may contain long stretches of solid rock without anyfissures or currents, the object of the invention is to produce a newtype of flowmeter which makes it possible to search even deep holes andlocate the areas containing currents for more elaborate furtherinvestigation.

As for the features characteristic of the invention, reference is madeto the claims.

SUMMARY OF THE INVENTION

The flowmeter of the invention comprises suitable flexible and elasticparting elements by means of which the section to be measured isseparated from the hole substantially pressure-tightly. In other words,the parting elements are made of an elastic material that is pressedagainst the surfaces of the hole under measurement, such that they aretightly pressed against the hole without any inflatable or expandablestructures activated by means of a pressure medium. Moreover, theflowmeter is provided with an open flow duct forming a free flowconnection past the section under measurement delimited by the partingelements, so that currents occurring in other parts of the hole will notproduce any pressure differences against the parting elements and thesewill, with a relatively low pressure, sufficiently seal off the holesection to be searched. In addition, the flowmeter comprises a measuringduct leading from the section under measurement to a point outside itand provided with measuring instruments by means of which the total flowof currents flowing into or out of the section can be measured.

The flexible and elastic parting elements used are preferablyplate-shaped or ring-shaped rubber or plastic discs with a free externaldiameter somewhat larger than the diameter of the hole to be searched.Moreover, in a hole measured from a direct radial direction, the rubberor plastic discs preferably have a shape turned or curved somewhatupwards, permitting easy descent of the flowmeter down the hole by theagency of its own weight. At the measuring depth, the flowmeter ispulled back up through a small distance, causing the discs to buckleinto a different position. In this condition, the internal tension ofthe parting element itself presses it against the hole surface,increasing its tightness.

The rubber discs of the invention acting as parting elements cannotwithstand a very large pressure. On the other hand, in this type ofmeasurement the pressure level in the section under measurement is thesame as in the rest of the hole, so there is no need for a highpressure-tightness. However, to ensure tightness, both parting elementsare made up of several, e.g. three successive rubber discs. Theprototype of the flowmeter of the invention was implemented using threerubber discs, which can withstand the pressure of a 11/2-meter watercolumn and therefore provide a sufficient tightness in all relevantmeasurement circumstances.

Especially when relatively large and sloping holes are being searched,the flowmeter's own weight may press the rubber discs to one side,causing the sealing to leak on the other side. In such applications itis preferable to use separate disc-shaped, plug-shaped or other similarrigid centering elements which, having a diameter nearly equal to thatof the hole, prevent significant radial motion of the flowmeter in thehole.

The measuring equipment preferably includes a suitable impulse sourceand sensors for measuring the direction and velocity of the impulsetransmitted by the impulse source.

The length of the bore hole section measured by the flowmeter of theinvention is preferably freely adjustable. This can be achieved e.g. byusing suitable extension pieces, of which a desired number can bemounted between the parting elements. In this way, the length of thehole section measured at a time may vary e.g. from one meter to over tenmeters. Therefore, the hole can be first searched in very long sections,whereupon the sections containing currents can be checked in shortersections. Hole portions that require slower and more precise flowmeasurements using more accurate equipment can thus be located with anaccuracy of e.g. one meter.

It is also possible to implement the flowmeter using a telescopicstructure in the meter body between the parting elements to allowadjustment of its length.

The flowmeter of the invention has significant advantages over prior-arttechnology. The flowmeter allows very fast measurement of holes severalkilometers in length, making it possible to locate hole portionscontaining currents, which are then examined more closely using otherequipment. Thus, as compared to prior art, the time required formeasuring and examining a single hole is reduced from months to a fewdays.

DETAILED DESCRIPTION OF THE INVENTION

In the following, the invention is described by referring to theattached drawing, which presents a diagram representing a flowmeter asprovided by the invention.

The flowmeter of the invention as presented in the drawing comprises anopen pipe 7 with three ring-shaped, elastic parting elements 1 at eachend, forming between them a measurement section 3 in the hole 2. Thepipe 7 forms an open flow duct 4 past the measurement section 3delimited by the parting elements 1 in the hole.

The parting elements 1 are elastic and flexible rubber flanges which,slightly deviating from the direction of the radius of the hole, extendobliquely upwards. Their size is so chosen that their elasticity willcause them to press against the round surface of the hole, in otherwords, their free external diameter is somewhat larger than that of thehole.

The pipe 7 between the parting elements 1 is provided with two apertures8 which, however, do not communicate with the open flow channel 4, butform the starting point of a measuring duct 5 which runs inside the pipe7 to measuring equipment 6 and, through this equipment, opens into thehole portion above the flowmeter.

The measuring equipment 6 comprises an impulse source 10 placed in themeasuring channel, and, placed on either side of it, sensors 11 allowingthe impulse sent by the impulse source, i.e. the velocity and directionof motion of the impulse, to be measured.

Moreover, the flowmeter is provided with a hoisting and control cable 9by means of which the flowmeter can be raised and lowered in the holeunder measurement e.g. using a suitable winch and through which themeasurement information obtained from the measuring equipment 6 istransferred to suitable processing apparatus provided above ground.

The flowmeter is used as follows. The flowmeter, suspended by thehoisting and control cable 9, is lowered into the hole to be measured toa desired measuring depth. At this depth, the flowmeter is pulled upthrough a short distance (a few centimeters), causing the plate-shapedparting elements to be pressed tightly against the hole surface. In thisway, a section 3 to be measured has been separated from the hole withsufficient sealing. To ensure that the parting elements will not beaffected by currents and pressure differences outside the measurementsection 3, pipe 7 provides a free flow path (arrows A) for externalcurrents past the measurement section 3.

If the rock 12 within the area covered by the measurement section 3contains any fissures 13 with currents (arrow B) in them, these currentscan cause a flow through the apertures 8 into the measuring duct 5 andthrough it (arrow C) further outside the flowmeter.

The flow rates in the measuring duct 5 may show large variations, whichis why flow measurement is performed by two methods. First, flowmeasurement is started by an impulse method, in which the water isheated momentarily by means of a heating thermistor 10 and the movementof the heat impulse produced by it in the water is monitored by means ofsensors 11 placed on either side of the heating thermistor at a distancefrom it. As the cross-sectional area of the measuring duct 5 is known,both the magnitude and direction of the flow are obtained by thismethod. This method can be used to measure currents with flow ratesvarying from a few milliliters to three thousand milliliters per hour.

Above the upper limit stated above, the divergence of the measurementresults increases, and the flow is determined by using a cooling method.In the cooling method, the heating thermistor 10 is heated, whereuponits cooling down is monitored, because the cooling takes place thefaster the higher is the flow rate. By using the cooling method, it hasbeen possible to extend the measuring range to 60000 ml/h and beyond.

After the measurements on a given section have been finished, theflowmeter can be easily moved, raised or lowered to the next place, andmeasurements can thus be continued one section at a time over the wholelength of the bore hole.

In addition, the apparatus preferably comprises a pump for keeping thewater level in the hole under measurement at a constant height. This canbe implemented using a long surge pipe whose lower end is blocked whilethe upper end is open. With this solution, the pumping of the water iseffected from inside the surge pipe as the water in the hole flows intothe surge pipe placed on a constant height. The water level inside thepipe varies but remains at constant height in the hole, i.e. at thelevel of the upper end of the pipe.

The apparatus may further comprise a pump for pumping water into thehole while the hoisting and control cable is being pulled up. Thisprevents the water level from falling as a result of the cable beingraised. In this way, the pumps can be used to keep the pressureconditions as constant as possible throughout the measuring operation.

The particulars of the use of the flowmeter and the processing of thedata are in themselves known in the art, so they will not be explainedin detail in this context. They can be summarized at a general level bysaying that the measuring programs proper are contained in a measuringcomputer which sends control commands to a processor in the flowmeterand receives measurement results from the processor. The measurementresults are subjected to conversions as required and they are presentedon a display screen and saved in files. Moreover, the measuring computerreads the pressure data (air pressure and ground water level), controlsthe hose pump, reads the pulses of a cable counter and stops the winchon the basis of the cable counter pulses. The measuring programs of theprocessor are stored in the flowmeter's program storage. These programsare used to take care of measurement timing, selection of measuringchannels, control of analog/digital conversion and sending themeasurement results to above-ground equipment.

The invention has been described above in detail by the aid of theattached drawing, but different embodiments of the invention arepossible within the scope of the inventive idea defined by the claims.

I claim:
 1. Flowmeter for locating zones containing currents in a bore hole made in a rock, wherein the flowmeter comprisesflexible and elastic parting elements (1) for separating a measurement section (3) in the hole from the rest of the hole in a substantially pressure-tight manner, an open flow duct (4) forming a free flow link between the hole portions on opposite sides of the flowmeter past the measurement section, a measuring duct (5) leading from the section under measurement to a point outside it, together with measuring equipment (6), for measuring the magnitude and direction of flow between the measurement section and the hole portion outside it, and wherein the parting elements (1) comprise plate-shaped rubber or plastic discs.
 2. Flowmeter as defined in claim 1, characterized in that, in the vertical hole under measurement, the edges of the rubber or plastic discs are bent upwards.
 3. Flowmeter as defined in claim 1, characterized in that a parting element comprises at least two, preferably three rubber discs (1) placed on top of each other.
 4. Flowmeter as defined in claim 1, characterized in that the measuring equipment (6) comprises an impulse source (10) and sensors (11) for measuring the direction and velocity of an impulse sent by the impulse source.
 5. Flowmeter as defined in claim 1, characterized in that a body of the flowmeter between the parting elements (1) comprises of a hollow pipe (7) which acts as a flow duct (4).
 6. Flowmeter as defined in claim 5, characterized in that the pipe (7) is provided with an aperture (8) between the parting elements (1), from which aperture the measuring duct starts, extending inside the pipe to measuring equipment (6) on the other side of the parting element.
 7. Flowmeter as defined in claim 1, characterized in that the flowmeter is provided with adjusting elements for the adjustment of the distance between the parting elements (1), i.e. the length of the hole portion to be measured.
 8. Flowmeter as defined in any one of claim 1, characterized in that the flowmeter is connected via a hoisting and control cable (9) to a hoisting device and a measurement data processing apparatus outside the hole.
 9. Flowmeter as defined in claim 1, characterized in that in conjunction with the flowmeter there is equipment for keeping the water level at a constant height in the hole during different stages of measurements and during transfer of the flowmeter in the hole.
 10. Flowmeter as defined in claim 2, characterized in that a parting element comprises at least two, preferably three rubber discs (1) placed on top of each other. 